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# Ajv: Another JSON Schema Validator
The fastest JSON Schema validator for Node.js and browser. Supports draft-04/06/07.
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## Please [sponsor Ajv](https://github.com/sponsors/epoberezkin)
Dear Ajv users! â¤ï¸
I ask you to support the development of Ajv with donations. ð
Since 2015 Ajv has become widely used, thanks to your help and contributions:
- **90** contributors ð
- **5,000** dependent npm packages âï¸
- **7,000** github stars, from GitHub users [all over the world](https://www.google.com/maps/d/u/0/viewer?mid=1MGRV8ciFUGIbO1l0EKFWNJGYE7iSkDxP&ll=-3.81666561775622e-14%2C4.821737100000007&z=2) âï¸
- **5,000,000** dependent repositories on GitHub ð
- **120,000,000** npm downloads per month! ð¯
Your donations will fund futher development - small and large improvements, support of the next versions of JSON Schema specification, and, possibly, the code should be migrated to TypeScript to make it more maintainable.
I will greatly appreciate anything you can help with to make it happen:
- a **personal** donation - from $2 âï¸
- your **company** donation - from $10 ð
- a **sponsorship** to get promoted on Ajv or related packages - from $50 ð°
- an **introduction** to a sponsor who would benefit from the promotion on Ajv page ð¤
| Please [make donations via my GitHub sponsors page](https://github.com/sponsors/epoberezkin)<br>â¼ï¸ **GitHub will DOUBLE them** â¼ï¸ |
|---|
#### Open Collective sponsors
<a href="https://opencollective.com/ajv"><img src="https://opencollective.com/ajv/individuals.svg?width=890"></a>
<a href="https://opencollective.com/ajv/organization/0/website"><img src="https://opencollective.com/ajv/organization/0/avatar.svg"></a>
<a href="https://opencollective.com/ajv/organization/1/website"><img src="https://opencollective.com/ajv/organization/1/avatar.svg"></a>
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<a href="https://opencollective.com/ajv/organization/3/website"><img src="https://opencollective.com/ajv/organization/3/avatar.svg"></a>
<a href="https://opencollective.com/ajv/organization/4/website"><img src="https://opencollective.com/ajv/organization/4/avatar.svg"></a>
<a href="https://opencollective.com/ajv/organization/5/website"><img src="https://opencollective.com/ajv/organization/5/avatar.svg"></a>
<a href="https://opencollective.com/ajv/organization/6/website"><img src="https://opencollective.com/ajv/organization/6/avatar.svg"></a>
<a href="https://opencollective.com/ajv/organization/7/website"><img src="https://opencollective.com/ajv/organization/7/avatar.svg"></a>
<a href="https://opencollective.com/ajv/organization/8/website"><img src="https://opencollective.com/ajv/organization/8/avatar.svg"></a>
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## Using version 6
[JSON Schema draft-07](http://json-schema.org/latest/json-schema-validation.html) is published.
[Ajv version 6.0.0](https://github.com/epoberezkin/ajv/releases/tag/v6.0.0) that supports draft-07 is released. It may require either migrating your schemas or updating your code (to continue using draft-04 and v5 schemas, draft-06 schemas will be supported without changes).
__Please note__: To use Ajv with draft-06 schemas you need to explicitly add the meta-schema to the validator instance:
```javascript
ajv.addMetaSchema(require('ajv/lib/refs/json-schema-draft-06.json'));
```
To use Ajv with draft-04 schemas in addition to explicitly adding meta-schema you also need to use option schemaId:
```javascript
var ajv = new Ajv({schemaId: 'id'});
// If you want to use both draft-04 and draft-06/07 schemas:
// var ajv = new Ajv({schemaId: 'auto'});
ajv.addMetaSchema(require('ajv/lib/refs/json-schema-draft-04.json'));
```
## Contents
- [Performance](#performance)
- [Features](#features)
- [Getting started](#getting-started)
- [Frequently Asked Questions](https://github.com/epoberezkin/ajv/blob/master/FAQ.md)
- [Using in browser](#using-in-browser)
- [Command line interface](#command-line-interface)
- Validation
- [Keywords](#validation-keywords)
- [Annotation keywords](#annotation-keywords)
- [Formats](#formats)
- [Combining schemas with $ref](#ref)
- [$data reference](#data-reference)
- NEW: [$merge and $patch keywords](#merge-and-patch-keywords)
- [Defining custom keywords](#defining-custom-keywords)
- [Asynchronous schema compilation](#asynchronous-schema-compilation)
- [Asynchronous validation](#asynchronous-validation)
- [Security considerations](#security-considerations)
- [Security contact](#security-contact)
- [Untrusted schemas](#untrusted-schemas)
- [Circular references in objects](#circular-references-in-javascript-objects)
- [Trusted schemas](#security-risks-of-trusted-schemas)
- [ReDoS attack](#redos-attack)
- Modifying data during validation
- [Filtering data](#filtering-data)
- [Assigning defaults](#assigning-defaults)
- [Coercing data types](#coercing-data-types)
- API
- [Methods](#api)
- [Options](#options)
- [Validation errors](#validation-errors)
- [Plugins](#plugins)
- [Related packages](#related-packages)
- [Some packages using Ajv](#some-packages-using-ajv)
- [Tests, Contributing, History, Support, License](#tests)
## Performance
Ajv generates code using [doT templates](https://github.com/olado/doT) to turn JSON Schemas into super-fast validation functions that are efficient for v8 optimization.
Currently Ajv is the fastest and the most standard compliant validator according to these benchmarks:
- [json-schema-benchmark](https://github.com/ebdrup/json-schema-benchmark) - 50% faster than the second place
- [jsck benchmark](https://github.com/pandastrike/jsck#benchmarks) - 20-190% faster
- [z-schema benchmark](https://rawgit.com/zaggino/z-schema/master/benchmark/results.html)
- [themis benchmark](https://cdn.rawgit.com/playlyfe/themis/master/benchmark/results.html)
Performance of different validators by [json-schema-benchmark](https://github.com/ebdrup/json-schema-benchmark):
[![performance](https://chart.googleapis.com/chart?chxt=x,y&cht=bhs&chco=76A4FB&chls=2.0&chbh=32,4,1&chs=600x416&chxl=-1:|djv|ajv|json-schema-validator-generator|jsen|is-my-json-valid|themis|z-schema|jsck|skeemas|json-schema-library|tv4&chd=t:100,98,72.1,66.8,50.1,15.1,6.1,3.8,1.2,0.7,0.2)](https://github.com/ebdrup/json-schema-benchmark/blob/master/README.md#performance)
## Features
- Ajv implements full JSON Schema [draft-06/07](http://json-schema.org/) and draft-04 standards:
- all validation keywords (see [JSON Schema validation keywords](https://github.com/epoberezkin/ajv/blob/master/KEYWORDS.md))
- full support of remote refs (remote schemas have to be added with `addSchema` or compiled to be available)
- support of circular references between schemas
- correct string lengths for strings with unicode pairs (can be turned off)
- [formats](#formats) defined by JSON Schema draft-07 standard and custom formats (can be turned off)
- [validates schemas against meta-schema](#api-validateschema)
- supports [browsers](#using